Py2neo 2020.1.0

• Added support for Neo4j 4.1
• Added experimental routing support
• Removed node and relationship caches
• Removed Graph/GraphService instance reuse
• Added test to ensure correct operation with multiprocessing
• Improved connection management and logging
• Added explicit "readonly" transaction mode
• Added triples method to OGM RelatedObjects
• Fixed cursor preview bug with empty results